Epidermal growth factor

EGF, a 6 kDa, 53 amino acid unglycosylated peptide, was one of the first growth factors discovered. Its existence was initially noted in the 1960s, as a factor present in saliva which could promote premature tooth eruption and eyelid opening in neonatal mice. EGF has subsequently proven to exert a powerful mitogenic effect on many cell types, and its receptor (Figure 10.7) is expressed by most cells. Its influence on endothelial cells, epithelial cells and fibroblasts is particularly noteworthy, and the skin appears to be its major physiological target. It stimulates growth

Figure 10.7 The EGF receptor. The N-terminal, extracellular region of the receptor contains 622 amino acids. It displays two cysteine-rich regions, between which the ligand-binding domain is located. A 23 amino acid hydrophobic domain spans the plasma membrane. The receptor cytoplasmic region contains some 542 amino acids. It displays a tyrosine kinase domain, which includes several tyrosine autophosphorylation sites, and an actin-binding domain that may facilitate interaction with the cell cytoskeleton

Figure 10.7 The EGF receptor. The N-terminal, extracellular region of the receptor contains 622 amino acids. It displays two cysteine-rich regions, between which the ligand-binding domain is located. A 23 amino acid hydrophobic domain spans the plasma membrane. The receptor cytoplasmic region contains some 542 amino acids. It displays a tyrosine kinase domain, which includes several tyrosine autophosphorylation sites, and an actin-binding domain that may facilitate interaction with the cell cytoskeleton

Table 10.11 Range of cells producing PDGF, and its major biological activities

Synthesized by

Platelets Fibroblasts Astrocytes Myoblasts

Vascular smooth muscle cells

Macrophages Endothelial cells Megakaryocytes Kidney epithelial cells Many transformed cell types

Biological activities mitogen for:

Fibroblasts Smooth muscle cells

Variety of transformed cells Glial cells chemo attractant for:

Fibroblasts Neutrophils

Monocytes Smooth muscle cells of the epidermal layer. Along with several other growth factors, EGF plays a role in the wound healing process, rendering a potential medical application obvious.

EGF may also find a novel agricultural application in the defleecing of sheep. Administration of EGF to sheep has a transient effect on the wool follicle bulb cell, which results in a weakening of the root that holds the wool in place. Although novel, this approach to defleecing is unlikely to be economically attractive.

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